A test socket electrically connects an Integrated Circuit (IC) device to a Printed Circuit Board (PCB) coupled to an IC tester. The IC tester provides electrical stimuli through the test socket to input contacts of the IC and receives electrical responses for analysis from output contacts of the IC through the test socket. As a result of the analysis, the IC tester may sort the IC into different categories, such as pass or fail, according to device specifications, or sort the IC into different grades, such as by measured response characteristics.
FIG. 1 illustrates a block diagram of a prior art test system for testing an IC 200, such as a Ball Grid Array (BGA) device, a Pin Grid Array (PGA) device, a Land Grid Array (LGA) device, and other devices having a plurality of electrical contacts organized in an array. An IC tester 400 is electrically connected to contacts on a PCB 300 through a cable 450. A test socket 100, which is adapted to receive the IC 200, is mounted on the PCB 300 to electrically connect the contacts on the PCB 300 to corresponding contacts on the IC 200.
The test socket 100 has conductor pins, such as spring-loaded probe pins (also known as “pogo pins”), which are contained within a body structure that is mounted to the PCB 300. Compression mounted test sockets with spring-loaded probe pins are commonly used for IC testing, because they allow easier removal, replacement, and repair of the test sockets.
FIG. 2 illustrates a housing structure 120 of the prior art test socket 100 which electrically connects contacts 230 of the IC 200 to corresponding contacts 330 of the PCB 300 when the IC 200 is received by the housing structure 120 and the housing structure 120 is mounted on the PCB 300. For examples of corresponding contacts, the contacts of the IC 200 that receive power are electrically connected to the contacts of the PCB 300 that provide power, the contacts of the IC 200 that are to be connected to ground are electrically connected to the contacts of the PCB 300 that are also connected to ground, the contacts of the IC 200 that receive input signals are electrically connected to the contacts of the PCB 300 that transmit those input signals, and the contacts of the IC 200 that transmit output signals are electrically connected to the contacts of the PCB 300 that receive those output signals.
In the example shown in FIG. 2, when the IC 200 is received in the housing structure 120, the IC's contacts 230 are vertically aligned with the PCB's contacts 330. The housing structure 120 comprises a top housing 140 and a bottom housing 150 for securing vertically held conductor pins 130 which make mechanical and electrical connections with corresponding pairs of the IC contacts 230 and the PCB contacts 330.
As one example of the conductor pin 130, a double-ended pogo pin is suitable for making a mechanical and electrical connection between aligned contacts of the IC 200 and PCB 300. FIGS. 3A and 3B respectively illustrate an example of a double-ended pogo pin 1300 in a non-compressed state and a compressed state. The double ended pogo pin 1300 has oppositely extending pin contacts 1310 and 1320 that are depressible within a barrel 1360 against internal compression spring 1350 which exerts a restoring force against plungers 1330 and 1340 of the pin contacts 1310 and 1320. To minimize transmission delays and cross talk between input/output contacts of the IC 200 and PCB 300, a miniature conductor pin that provides a low profile connection between corresponding contacts of the IC 200 and the PCB 300 may be useful. U.S. Pat. No. 6,046,597 describes an example of such a miniature conductor pin, as well as a prior art test socket such as described herein.
FIG. 4 illustrates a partial cross-sectional view of the prior art housing structure 120 of the test socket 100. As previously noted, the housing structure 120 comprises a top housing 140 and a bottom housing 150. To secure the conductor pins 130 in the housing structure 120, the top housing 140 has counterbore holes 145 which are sized to allow the top pin contacts (e.g., 1310) of the conductor pins 130 to pass through the top housing 140 to make mechanical and electrical connections with corresponding contacts of the IC 200, but prevents the barrels (e.g., 1360) of the conductor pins 130 from passing through. Likewise, the bottom housing 150 also has counterbore holes 155 which are sized to allow the bottom pin contacts (e.g., 1320) of the conductor pins 130 to pass through the bottom housing 150 to make mechanical and electrical connections with corresponding contacts of the PCB 300, but prevents the barrels (e.g., 1360) of the conductor pins 130 from passing through. Thus, when the top and bottom housings, 140 and 150, are attached to each other, the conductor pins 130 are vertically restrained by the attached top and bottom housings, 140 and 150.
As may be readily appreciated, the total height (or thickness) of the housing structure 120 is related to the length of the conductor pins which it is holding. As previously mentioned, shorter conductor pins may provide benefits for IC testing, such as minimizing transmission delays and cross-talk between input/output signals. To accommodate shorter conductor pins, a relatively thinner housing structure is generally used. However, although the total height of the housing structure 120 may be limited to accommodate the length of the conductor pins which it is holding, some flexibility is available in selecting the thicknesses of the top and bottom housings, 140 and 150, which add up to the total height. For illustrative purposes, in FIG. 4, the total height of the housing structure 120 is indicated by T1, the thickness of the top housing structure is indicated by T2, and the thickness of the bottom housing is indicated by T3.
Although FIG. 4 illustrates an example of a housing structure 120 which has approximately equal thicknesses for the top and bottom housings, 140 and 150, it may be desirable to have a thicker top housing 140, because a thin top housing 140 is more likely to bow or bend under pre-load forces from the conductor pins 130 when the test socket 100 is mounted on the PCB 300. However, a thicker top housing 140 means a thinner bottom housing 150, because the overall height or thickness of the housing structure 120 should be the same to properly accommodate the lengths of the conductor pins 130 which they are holding. The thickness of the bottom housing 150, however, is limited to a minimum thickness, indicated by T4, which is required to accommodate the counterbore holes 155 of the bottom housing 150. In light of these considerations, a range of commonly used top and bottom housing thickness ratios is believed to be between a 1 to 1 ratio (i.e., T2/T3=1, as shown in FIG. 4) and a 3 to 1 ratio (i.e., T2/T3=3.0).
As IC devices increasingly provide more functionality, the number of their Input/Output (I/O) contacts increase accordingly and the pitch between their I/O contacts may decrease accordingly. Also, as IC devices operate at increasingly higher speeds and/or bandwidths, test sockets which are used to test such IC devices preferably should have low profiles to minimize transmission delays through, and cross-talk between, I/O contacts of the IC devices. However, spring load forces from spring-loaded conductor pins create a strain on the socket's housing that may limit a minimal thickness for such housing. Accordingly, it is desirable to provide an improved test socket structure which has a low profile (i.e., low total height or thickness) and suitable structural integrity for high speed and/or high frequency testing of IC devices employing densely populated I/O contacts.